The Sri Lankan cabinet is to amend the constitution, removing the president's powers to dissolve parliament a year after elections.

A government spokesman said an amendment would also be tabled allowing MPs to vote against their party without being expelled.

The spokesman also reiterated that peace talks with Tamil Tigers were likely to take place in late June - a day after the rebels warned a row over a key ceasefire accord could delay them.

Tigers want an independent Tamil state

The BBC's Colombo correspondent, Frances Harrison, says opposition MPs are vital to the government if the peace process is to succeed, as parliament must approve constitutional changes requiring a two-thirds majority.

But she says the moves are likely to increase friction in the cohabitation between the president and government.

Under the changes proposed by cabinet, the president will no longer be able to dissolve parliament without the consent of the prime minister or a majority of the house.

Government spokesman Professor GL Peiris denied the moves would antagonise President Kumaratunga.

But our correspondent says they do curtail her powers and make it easy for her supporters to defect without facing disciplinary action.

June talks

Asked when the government would meet the Tigers' last precondition and lift the ban on their organisation, Professor Peiris said a decision would be made very shortly.

Balasingham: Rebels "disappointed"

On Thursday, rebel chief negotiator Anton Balasingham had accused the government of not fully implementing its part of the February accord, and said the timetable for talks could slip further.

Mr Balasingham listed a number of key sticking points after talks in London with Norwegian mediators.

One of them was restrictions on fishing in Tamil areas, which are now reported to have been lifted.

Meanwhile, the government has decided to allow the Indian Oil Corporation to operate an oil tank farm used for refuelling ships passing the east coast town of Trincomalee.

There were no details of what security provisions would be taken for the oil tanks, which have until now been a high risk proposition because of the possibility of a rebel attack.